1. Field of the Invention
The present invention relates to a control technique for driving a motor used particularly for an image scanner or the like.
2. Description of Related Art
Business machines, such as an image scanner, a copying machine, an XY plotter, a printer, a facsimile machine, etc., are often arranged to switch the rotating direction of a motor between normal and reverse rotations for carrying out various work with reciprocating motions.
As one example of such a normal-and-reverse rotation conversible arrangement for the motor, an image scanner is arranged as shown in FIG. 9. Referring to FIG. 9, the image scanner 106 is arranged to scan and read information provided on an original P, by moving, with a motor (not shown), a light source 101 such as a xenon lamp or the like to the right, as viewed FIG. 9, in such a way as to serially illuminate the original P, which is placed on an original placing glass plate 100. Then, image light reflected from the original P is led through mirrors 102, 103 and 104 to an image sensor 105 which is composed of a CCD, etc. The image sensor 105 converts the image light into an electrical signal. The motor is then reversely driven to move the light source 101 to the left, as viewed in FIG. 9, so as to make preparation for scanning information provided on the next original.
In a case where the image scanner 106 is used as an image input device for a host computer, if a reading action is interrupted or discontinued while reading one page of an original is still in process, the motor is driven reversibly (backward) even if the motor is in process of normal (forward) rotation.
With the image scanner 106 used as an image input device for a host computer, the host computer first temporarily stores image data sent from the image scanner 106 in a buffer memory and then processes the image by gradually taking out the image data from inside of the buffer memory. In this instance, if the buffer memory is filled up with the image data while the image processing action is still in process, an overflow of the incoming data is prevented by sending a data-output-stop signal from the host computer to the image scanner 106 and the reading action is put to a pause. After that, the image scanner 106 is requested to restart sending the image data when the fear of overflow disappears.
At the time of restart of transmission of image data from the image scanner 106, if the reading action is allowed to be restarted from a position where the reading action has been put to the pause, an image obtained by reading tends to be affected by the vibrations of the optical system remaining in the image. To prevent such image deterioration, the image scanner 106 causes the motor to reversibly rotate to move the light source 101 backward to an extent of a predetermined distance of an approach run. Then, the motor is allowed to rotate again to gradually increase its rotation speed up to a rotation speed corresponding to a prescribed scanning (reading) speed. When the light source 101 reaches its interrupted position, the reading action is allowed to be resumed.
The driving force of the motor is transmitted through a transmission means such as gears, etc., to an optical system arranged for the light source 101, etc. However, in a case where the motor is caused to reversely rotate as mentioned above, backlash between teeth of an intermeshing pair of gears is arranged to be absorbed in the initial stage of reverse rotation driving.
However, since the rotation speed of the motor is gradually increased even while the backlash or the like is being absorbed, as shown in FIG. 10, a noise due to chattering of gears or face deflection vibrations has been generated over a long period of time. Particularly, in the case of reading many originals with the image scanner, frequent reverse rotation of the motor frequently brings about such a noise. Therefore, effective measures against the generation of the noise have been strongly desired.
It is a principal object of the invention to lessen the noise taking place when a motor is reversely rotated due to a clearance in a transmission part which is arranged to transmit the driving force of the motor.
To attain the above object, in accordance with an aspect of the invention, there is provided a motor control apparatus for driving and controlling a motor so as to transmit a rotating force of the motor through a plurality of transmission means, the motor control apparatus comprising control means for, when reversing a rotation of the motor, causing the motor to rotate at a speed higher than a normal rotation speed only for a period of time which is substantially the same as a period of time required for absorbing a clearance existing between the plurality of transmission means.
Such an arrangement of the motor control apparatus effectively lessens the noise generated in reversing the rotation of the motor due to a clearance in the motor driving force transmitting part.
The above and other objects and features of the invention will become apparent from the following detailed description of preferred embodiments thereof taken in connection with the accompanying drawings.